Cranks Anonymous

Sean Carroll, blogger-in-chief at Cosmic Variance, has ventured abroad from his palatial Californian residence and is currently slumming it in a little town called Oxford where he is attending a small conference in celebration of the 70th birthday of George Ellis. In fact he’s been posting regular live commentaries on the proceedings which I’ve been following with great interest. It looks an interesting and unusual meeting because it involves both physicists and philosophers and it is based around a series of debates on topics of current interest. See Sean’s posts here, here and here for expert summaries of the three days of the meeting.

Today’s dispatches included an account of George’s own talk which appears to have involved delivering a polemic against the multiverse, something he has been known to do from time to time. I posted something on it myself, in fact. I don’t think I’m as fundamentally opposed as Geroge to the idea that we might live in a bit of space-time that may belong to some sort of larger collection in which other bits have different properties, but it does bother me how many physicists talk about the multiverse as if it were an established fact. There certainly isn’t any observational evidence that this is true and the theoretical arguments usually advanced are far from rigorous.The multiverse certainly is a fun thing to think about, I just don’t think it’s really needed.

There is one red herring that regularly floats into arguments about the multiverse, and that concerns testability. Different bits of the multiverse can’t be observed directly by an observer in a particular place, so it is often said that the idea isn’t testable. I don’t think that’s the right way to look at it. If there is a compelling physical theory that can account convincingly for a realised multiverse then that theory really should have other necessary consequences that are testable, otherwise there’s no point. Test the theory in some other way and you test whether the multiverse emanating from it is sound too.

However, that fairly obvious statement isn’t really the point of this piece. As I was reading Sean’s blog post for today you could have knocked me down with a feather when I saw my name crop up:

Orthodoxy is based on the beliefs held by elites. Consider the story of Peter Coles, who tried to claim back in the 1990’s that the matter density was only 30% of the critical density. He was threatened by a cosmological bigwig, who told him he’d be regarded as a crank if he kept it up. On a related note, we have to admit that even scientists base beliefs on philosophical agendas and rationalize after the fact. That’s often what’s going on when scientists invoke “beauty” as a criterion.

George was actually talking about a paper we co-wrote for Nature in which we went through the different arguments that had been used to estimate the average density of matter in the Universe, tried to weigh up which were the more reliable, and came to the conclusion that the answer was in the range 20 to 40 percent of the critical density. There was a considerable theoretical prejudice at the time, especially from adherents of inflation, that the density should be very close to the critical value, so we were running against the crowd to some extent. I remember we got quite a lot of press coverage at the time and I was invited to go on Radio 4 to talk about it, so it was an interesting period for me. Working with George was a tremendous experience too.

I won’t name the “bigwig” George referred to, although I will say it was a theorist; it’s more fun for those working in the field to guess for themselves! Opinions among other astronomers and physicists were divided. One prominent observational cosmologist was furious that we had criticized his work (which had yielded a high value of the density). On the other hand, Martin Rees (now “Lord” but then just plain “Sir”) said that he thought we were pushing at an open door and was surprised at the fuss.

Later on, in 1996, we expanded the article into a book in which we covered the ground more deeply but came to the same conclusion as before. The book and the article it was based on are now both very dated because of the huge advances in observational cosmology over the last decade. However, the intervening years have shown that we were right in our assessment: the standard cosmology has about 30% of the critical density.

Of course there was one major thing we didn’t anticipate which was the discovery in the late 1990s of dark energy which, to be fair, had been suggested by others more prescient than us as early as 1990. You can’t win ’em all.

So that’s the story of my emergence as a crank, a title to which I’ve tried my utmost to do justice since then. Actually, I would have liked to have had the chance to go to George’s meeting in Oxford, primarily to greet my ertswhile collaborator whom I haven’t seen for ages. But it was invitation-only. I can’t work out whether these days I’m too cranky or not cranky enough to get to go to such things. Looking at the reports of the talks, I rather think it could be the latter.

Just in case it was not absolutely clear, George’s anecdote (and my retelling thereof) were meant to be critical of the unnamed elitist bigwig, and favorable toward he and Peter, who were after all right. (It should be clear, but this is the internet, and meaning doesn’t seem to travel well.)

Anton, I don’t know who the bigwig was and don’t care to guess, but I could certainly see how such a comment from a senior person to a junior person could be received as a threat rather than as helpful pointer.

Anton: it’s so long ago I can’t remember the exact words, but the comment was made in a far-from-friendly tone of voice and at the time I took the intent to be threatening. Not that I felt particularly threatened; I just thought it was a bit sad. I had a big laugh about it with George actually.

Sean: I think it’s clear that you were repeating George’s story – which I’ve heard him tell from time to time myself. I don’t mind it at all. In fact I still find the story very funny! It also serves well to make the point he was making rather well: that scientists can become blinkered by orhodoxy in spite of the evidence.

Interestingly, I recall George making similar remarks (ie people were taking their ides too seriously) about wormholes back in the early 90s. If memory serves correctly, someone (I think Bill Unruh, but the Scotch may have destroyed too many brain cells over the years) had received a rejection of a paper in which he was critical of the then current infatuation with wormholes. One reviewer commented that the paper ran counter to the well established laws of wormhole physics. This remark was met with combined chortling and indignation.

George has a great and admirable ability for keeping people firmly attached to the ground.

Oh, can I take this opportunity to ask a geeky cosmology question that has been rattling around in the back of my mind for almost exactly a decade.

Before supernova results and before bomerang and wmap etc there were people that wanted omega to equal 1 and the universe to be flat and there were people saying “omega only seems to equal 0.3 whether you like it or not” which is pretty much the position you take in your book “is the universe open or closed”.

One solution (which is what is now believed) would be that omega does equal 0.3 but that the other 0.7 is made up by some sort of lamda value (now called dark energy). At the time you might have thought this would be the perfect compromise – that the flat universe people could have their flat universe and the omega equals 0.3 people could have there omega equaling 0.3.

So why wasn’t it taken very seriously in the late 90s? Most books of that time couldn’t mention the possibility without a few lines later using the words “Ad-hoc” which is fair enough – including a term for no other reason than to solve another problem.

But in your book, there was another reason that you rejected the idea and if memory serves it had something to do with papers published about the distribution of quasars in the sky or something like that – it was a statistical argument.

What became of that argument? Where did they go wrong? Have people gone back to do a post mortem?

I’m not sure I should reply to someone who admits to hating almost everything that is good about the world, but since I’m a nice fellow I’ll try.

First I should say that we had decided at the outset to try to focus just on the matter density rather than let the book become a general discussion of all the cosmological parameters. However, since observational quantities generally depend on more than one parameter it proved necessary to talk a little about other ones, especially Lambda.

There were indeed people around in the early 90s who accepted that Omega was 0.3 and postulated dark energy to make up the difference.
George wasn’t all that impressed by inflation so never really felt very strongly about a flat universe anyway.

Until the supernovae and CMB data came in there weren’t really strong constraints on this model. In the book we referred to results from Chris Kochanek and collaborators who put limits on Lambda on the basis of the number of gravitationally lensed quasars observed. This depends strongly on the volume out to a given redshift which in turn depends strongly on lambda. Models with a large lambda seemed to predict many more lensed quasars than actually observed. In the book we said “..unless some significant error is present in the modelling procedure adopted in these studies” then these suggest a smaller lambda than the 0.7 needed to render the universe flat. I haven’t looked at this particular thing again to see precisely what went wrong, but it is fair to say that views about the internal structure of a galaxy halo have changed quite a bit in the intervening time. I’d welcome other comments on this.

I should also mention that in the book we also discussed the first SN1a results which were brand new at the time; the paper was Perlmutter et al. 1996, in press in our references!. Only 7 high-redshift objects were included and they didn’t show definite evidence of a lambda. Things changed when they got more data a few years down the line.

“Until the supernovae and CMB data came in there weren’t really strong constraints on this model”

I think this is misleading. The most important pointer towards Lambda was the *lack* of any detection of CMB fluctuations – principally by the sensitive Owens Valley experiments of the late 1980s. That does count as “CMB data”, but I suspect not in the sense you meant. When you add this non-detection to the evidence for a low matter density, you have to go for a Lambda-dominated model. George Efstathiou and friends saw this with exquisite clarity in 1990 (Nature 348 705).

The reason people didn’t just accept it was that non-zero Lambda seemed crazy (and perhaps it still does). Extra evidence was needed. When the first supernova results in 1996 firmly ruled out Lambda (something they now don’t like to have remembered), things seemed very confused. It was only when the second round of SNe papers got a different answer that I gave up fighting Lambda and decided to live with it.

So, if you want to allocate credit for the discovery of dark energy, Owens Valley and Efstathiou et al. deserve to be around the top of the list.

Definitely the paper you refer to should be acknowledged and we did so in our paper. However, there was always the cowards’ way out of the CMB non-detection problem, i.e. to concoct a designer primordial spectrum that gave structure where you wanted it and not where you didn’t. And in those days some of us also wrote crazy papers about large-scale bias or anti-bias that might break the connection between clustering and the CMB. Now we have galaxy and CMB spectra that chime with each other whereas 20+ years ago we had only upper limits on the CMB and relatively small-scale clustering measurements. Bridging the two required some sort of assumptions and people found reasons not to make the obvious ones.

Looking back it does look obvious that Lambda was the right choice – but that just underlines the achievements of those that saw it at the time. I was certainly allergic to Lambda – I still am to some extent – but its emergence in the standard model after all that prejudice says something about the strength of the evidence we now have.

thanks, that was really interesting. And surely not that embarrassing either. Both pc and jp give low omega and reasonably high H – both of which are now thought correct and that gives reasonably large values for the age of the universe. You just weren’t bothered about inflation so no reason to include lambda. The good thing about a low density parameter (apart from being right!) was you had so much more flexibility in terms of possible H and therefore age of the universe so that you could just follow the best evidence.

With hindsight isn’t it the theorists who WERE keen on inflation who were more baffling. None of them ever “needed” an omega of 1, what they needed was a flat universe – omega + lambda = 1. But in the years following when this picture was taken they were fighting at least 3 losing battles weren’t they?

– the evidence (as shown in your book) for a low density parameter. The observational (as opposed to theoretical) evidence for omega(matter density) = 1 was pretty much non existent, wasn’t it? There never was a baryon “catastrophe”!

– and even if H WAS low, their age of the universe was still bumping into the age of the oldest stars. H needed to be below 50 to give a universe older than 13 billion years I think. They obviously wanted the oldest stars to turn out to be younger.

They were bending over backwards to get a omega larger than indicated, an H lower than indicated and stars younger than indicated.

All these would vanish at once AND they wouldn’t lose any of the force of their inflation argument if only they were prepared to swallow a non zero lambda.

Instead of going around threatening men with beards and pony tails, they could have used their die-hard adherence to a universe that was flat to predict one that was also accelerating.

Is this unfair? I could understand it better if there were other reasons putting them off lambda. This was why I was so interested if there ever was any evidence against a non zero lambda or was it entirely due to the aversion to its “craziness”.

Sorry if I suggested you attached more weight to Chris Kochanek and collaborators than you actually did – I read it a long time ago – and only mentioned it because it was the only place I ever saw any such evidence. The 2nd being the the post above about the original 1996 supernova evidence. Was there ever anything else?

I only studied cosmology as undergraduate so the above is probably oversimplified or just wrong! And anyway, there are lots of “should”s and “could”s above, I suppose in the end when the evidence was strong people came round to the new model and that is how science should change.